IFLScience's Perseverance's Latest Mars Rock Sample Contains Curious "Greenish" Mineral begins:

Having long broken its record of firsts on Mars, the Perseverance rover, still pootling around sciencing the sh*t out of the Red Planet, has just locked and loaded its third sample to send home to Earth. Peering inside a rock, Percy scraped a small patch to get a look at something no one has ever seen before: what lies under the surface layer. In this case, it appears rock that carries a curious greenish mineral known as olivine.

"Another little piece of Mars to carry with me," the rover's representatives on Earth revealed on social media. "My latest sample is from a rock loaded with the greenish mineral olivine, and there are several ideas among my science team about how it got there. Hypotheses are flying! Science rules."

I don't mean to suggest that Perseverance is being anal retentive, but rather than carrying all these samples around, isn't the point to cache them along the way?

Or is the plan now to hang on to all of them and just deliver them to the launch site for the sample return mission?

I'm soooo... confused!

Question: Is Perseverance going to keep carrying those samples around or cache them? I don't really understand the plan.

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    $\begingroup$ One of the dangers of carring all the core for the duration of the mission is that with the movement of Percy there's a risk some of the core could fragment or even pulverize. This risks some of the core being lost during transfer & other movements. There is a potential for this to contaminate the other samples. The other thing is, even though the core has a small diameter, much can be learned from examining an intact piece of rock, as opposed to pebble fragments or dust. $\endgroup$
    – Fred
    Commented Nov 18, 2021 at 10:33

1 Answer 1


You have to consider two things:

First, it is going to be easier for the Fetch Rover if the tubes are cached in a small number of locations. As shown in the surface operations descriptions, the efficient option is for Perseverance to carry some for a while and then cache them together. There is more detail in this article:

Instead of dropping off each sample tube once it’s processed, the current expected strategy is to place the processed sample tube into storage until enough samples are collected in a particular region of interest, at which point a group of samples will be dropped off at a designated location for caching.

Second, redundancy. It is risky to rely on just one rover to do the delivery, so, as shown in slide 19 of this presentation, the safe option is to have both Perseverance bring some back to the launch site and for the Fetch Rover to go and pick up caches.

So, the answer is 'some and some'. It will carry them around for some time, then, when there are enough (presumably the number is decided by the mission team), a group will be dropped off. And some will remain on Perseverance for delivery to the launch site.

  • $\begingroup$ Sorry, I thought that was implicit: At any time, it is going to be carrying some around. When it has enough (decided by the mission team, I guess) it will cache them. These will be picked up by SFR. But, there will also be some that it delivers to the lander itself. $\endgroup$ Commented Nov 18, 2021 at 17:47
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    $\begingroup$ Well, "Is Perseverance going to keep carrying those samples around or cache them?" - the answer over the whole mission is 'some and some'. If you meant specifically the 2 or 3 it has already, then I don't know if it has the ability to selectively cache or if it has to drop all those it is currently carrying in one go. $\endgroup$ Commented Nov 18, 2021 at 17:54
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    $\begingroup$ OK - added a summary - and a useful paper that I found in the meantime. $\endgroup$ Commented Nov 18, 2021 at 19:10

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